The invention relates to pallets used for material handling and storage and, in particular, to improvements in molded plastic pallets.
It is known to mold pallets of plastic and/or other materials thus departing from traditional wood slat construction. More specifically, it is known from U.S. Pat. No. 4,428,306 to Dresen et al. and U.S. Pat. No. 5,046,434 to Breezer et al., for example, to mold pallets of two sheets fused or otherwise joined together. The sheets are typically molded with shallow grooves to increase their individual stiffness. These patents teach that the main areas of the two sheets be arranged relatively close together and adjacent the top plane of the pallet. Commonly, pallets of this type have molded feet that depend downwardly from the main planes of the double sheets at locations spaced throughout the plan area of the pallet. These double sheet pallets with depending feet are limited in their rigidity and strength as a result of the relatively close proximity of the sheets. Moreover, a pallet of this style often cannot be practically stacked onto another loaded pallet because the legs or feet may not properly register with the goods or packages on the loaded pallet. Still further, the relatively small surface areas represented by the feet can produce relatively high unit pressure on the goods or containers on an underlying loaded pallet.
The invention provides an improved molded plastic pallet that achieves a high rigidity and strength for its material content or weight and that is readily stackable onto either a loaded pallet or onto an empty pallet. The disclosed pallet is comprised of a pair of sheets that are molded into unique configurations. The sheets provide upper and lower platforms with relatively large surface areas for adequately supporting a load and for stabilizing the pallet when it is stacked on a loaded pallet.
The sheets are molded with interfitting formations that support the upper platform or deck above the lower platform or base a vertical distance adequate to receive the carrying forks of a lift truck or a floor jack. The formations, likewise, are configured to provide generous horizontal clearance for reception of the forks while preventing undue distortion or structural failure under load.
More particularly, the formations are configured to adequately transfer the load on the upper deck to the carrying forks or to the base without buckling or other gross distortion.
The disclosed pallet is especially useful for transporting and storing conventional milk crates which typically are molded plastic and are generally cubic in shape. The pallet is arranged to carry such crates in 3xc3x973 layers (9 crates per layer) and with a stack height of 3 layers on each pallet. In this milk crate application, loaded pallets constructed in accordance with the invention can be stacked 3 pallets high with the base of successive loaded pallets safely and stably resting on the tops of the crates of an upper layer of an underlying loaded pallet. The pallet of the invention includes on the top deck a peripheral flange that horizontally locates and stabilizes the milk crates. Moreover, this upper flange is configured to receive a lower base flange of another identical pallet in a nesting fashion thereby facilitating stacking of empty pallets.
The disclosed pallet is preferably produced by forming the upper and lower sheets, made of thermoplastic material, into their configurations on shaped aluminum tools through application of heat, vacuum and/or pressure. Once molded to form, the sheets are pressed together using their forming tools as platens. This pressing operation is done while the sheets are at an elevated temperature thereby causing the sheets to fuse together at local surface areas of contact. The surface areas where fusion occurs, ideally, are provided with relief zones, typically in the nature of grooves in one of the sheets. The relief zones allow a small amount of sheet material to squish out from the contact areas to ensure that contact and fusion occurs at all intended fusion areas regardless of slight variations in material thickness, molded form, and/or relative positions of the tools when pressing the sheets together.